The present invention relates to a belt used in a continuously operated, conveyor-type thermal treatment of a material bed, i.e. in a sintering process, which belt is made of interconnected elements and provided with perforations for conducting the heating and possibly cooling gases to be fed in the material to be sintered advantageously through the material bed to be sintered and simultaneously through the belt.
In a continuously operated material sintering process, there is conducted hot gas through the material bed that is formed on the belt of the material to be sintered, which gas reacts with the material bed at a high temperature, for instance when the ferroalloy pellets form a material bed within the temperature range of 1,300-1,600xc2x0 C., so that the soft particles to be sintered are hardened and are thus easy to be processed further. After the sintering proper, the sintered particles are cooled, and cooling gases are conducted in the material bed during the cooling process. Thus the belt is subjected to both heating and cooling within an essentially short length, which essentially raises the criteria for high-standard qualities required of the belt.
From the U.S. Pat. No. 4,316,718, there is known an endless, perforated conveyor belt used for heat-treating a bed of material by feeding hot gas through said material bed. Gas can be fed through the bed either from above the bed or from underneath it. When gas is fed from above, it first penetrates the material bed and proceeds through the elongate slots provided in the conveyor belt. The slots are made in the centre of the conveyor belt in adjacent rows that are spaced apart. The rows made of elongate slots are mutually arranged so that the rows fall transversally to the proceeding direction of the conveyor belt. When the belt wears off in the heat treatment of the material bed, the endless conveyor belt must always be replaced as a whole. This increases the expenses of the heat treatment of the material bed, because a perforated conveyor belt as such is expensive to manufacture. In addition, the replacing of a whole conveyor belt takes a lot of time, which cuts the working time of the apparatus.
The object of the present invention is to eliminate the drawbacks of the prior art and to achieve a conveyor belt suited for a continuously operated thermal treatment of a material bed, i.e. for a continuously operated conveyor-type sintering of the material bed, which conveyor belt is economical in manufacturing costs and can also be replaced in parts. The essential novel features of the invention are apparent from the appended claims.
According to the invention, the conveyor belt used in a continuously operated conveyor-type thermal treatment, i.e. sintering, of a material bed is made of interconnected, at least one-part elements, and in each element, at least in the part that is in contact with the material bed formed on the conveyor belt, there are made perforations for conducting the gas needed in the thermal treatment through the conveyor belt via said perforations. The elements constituting the conveyor belt are advantageously made of metal, such as ferritic, austenitic or acid-proof steel by rolling, so that the rolling direction is either transversal or parallel to the proceeding direction of the conveyor belt. The conveyor belt perforations are mutually arranged so that said perforations advantageously form a row that is either transversal or parallel to the proceeding direction of the conveyor belt or forms an angle with respect to the proceeding direction of the conveyor belt.
A single element of the conveyor belt according to the invention compiled of elements consists of one or several pieces. In particular, if the element is essentially a uniform piece along the whole width of the conveyor belt, the element is usually made of one piece, which is installed in the conveyor belt transversally to the proceeding direction of the conveyor belt. Even then several one-piece elements can be interconnected transversally to the proceeding direction of the conveyor belt prior to attaching the arrangement compiled of several pieces as part of the conveyor belt.
A conveyor belt element can also include several pieces arranged in parallel to the proceeding direction of the conveyor belt, which pieces are first interconnected in the lengthwise direction and further attached as part of the conveyor belt transversally to the proceeding direction thereof. When the element is formed of pieces that are arranged in parallel to the proceeding direction of the conveyor belt, said pieces can be made either essentially equally thick, or for instance such that at the outer edges of the conveyor belt, there are installed pieces that are either thicker or thinner than the pieces installed in the middle of the conveyor belt.
The number of the perforations provided in the conveyor belt element according to the invention is such that as regards the area of the element consisting of one or several pieces, the total area of the perforations is 20-60%, advantageously 35-40%. Moreover, said perforations are arranged in groups in the lateral direction of the conveyor belt, so that at both edges of the conveyor belt, there is provided an perforation-free zone having the width of 20-25% of the total width of the conveyor belt. In addition, the perforations provided in the middle section of the conveyor belt, in between the two perforation-free edge zones, are positioned so that in between two perforated zones, there is provided a perforation-free zone having a width that is equal to the width of the perforated zones. In the perforated zone, the perforations are placed in one or several rows in the lateral direction of the conveyor belt. As such, the rows formed by the perforations can follow either the lateral or the lengthwise direction of the conveyor belt, or they can form an angle of about 30-60 degrees with respect to the proceeding direction of the conveyor belt.
In shape, the perforation made in the conveyor belt element can be for example circular or oval, or it can have some other shape. A perforation that represents some other shape than circular is advantageously placed, with respect to the conveyor belt, so that the larger dimension of said perforation is positioned in the lateral direction of the conveyor belt. The perforation can also be placed in the conveyor belt so that the smaller dimension of said perforation is positioned in the lateral direction of the conveyor belt. When the perforation represents some other shape than circular, the ratio of the perforation dimensions is advantageously within the range 0.1-0.5.
In a conveyor belt according to the invention, the perforated zone is made of mutually identical perforations that are advantageously arranged in one or several rows, and in each row the perforations are spaced apart. A perforated zone may also be formed of mutually different perforations, advantageously so that mutually identical perforations are arranged in their own rows, and other different perforations again in their own rows. The obtained different rows can advantageously be arranged for instance in an alternating fashion.
A conveyor belt element according to the invention is connected to another element in order to compile the conveyor belt proper advantageously in a mechanical fashion, such as by welding the conveyor belt in the lateral direction of the conveyor belt, i.e. transversally to the proceeding direction thereof. The junction can also be realised so that at one lateral edge of the conveyor belt element, there is installed at least one mechanical connecting piece, and at another lateral edge of the conveyor belt element, there is installed another mechanical connecting piece in order to create the junction.